Metal Organic Chemical Vapor Deposition (MOCVD) is a new vapor epitaxial growth technology developing on a basis of a vapor epitaxial growth. MOVCD has advantages such as an easily controllable growth, a growable highly-purified material and a large area of an epitaxial layer with good uniformity.
An MOCVD reactor is a main process apparatus for manufacturing a high light LED chip. Reference is made to FIG. 1 which is a schematic structural view of an MOCVD reactor in the conventional technology, for example. The MOCVD reactor includes a chamber 10, a heater 11 located at the bottom of the chamber 10, and a tray 13 located above the heater 11. The tray 13 is associated with a rotating mechanism by a supporting structure 12. The tray 13 is configured to support a substrate 14. The MOCVD reactor further includes a feeder 15 located at the top of the chamber 10.
In a working process of the MOCVD reactor, the feeder 15 inputs a raw material gas including an organic metal into the chamber 10, and the heater 11 is configured to heat to make the raw material gas dissociate, thereby forming a film on a surface of the substrate 14.
A working temperature in the MOCVD reactor is generally in a range from 500 to 1200 degree Celsius. A temperature control system for controlling a current of the heater 11 is provided in the MOCVD reactor in the conventional technology, to achieve the working temperature of the MOCVD.
Reference is made to FIG. 2, which is a schematic view of a temperature control system of the MOCVD reactor in the conventional technology, for example. The temperature control system of the MOCVD reactor includes a temperature controller 16. The temperature controller 16 includes two input terminals and one output terminal. The first input terminal is configured to input a set temperature value. The second input terminal is coupled with an upper surface of the tray 13 in the chamber 10 and configured to obtain an actual temperature of the upper surface of the tray 13 (in this example, the upper surface of the tray supports the substrate 14, thus the actual temperature of the upper surface of the tray is approximately to be the actual temperature of the substrate 14). The output terminal is connected to a direct current power supply of a heater 11. The temperature controller 16 is configured to compare the set temperature value with the actual temperature and calculate a control signal based on a difference therebetween. The output terminal sends the control signal to the direct current power supply of the heater 11 to control the current of the direct current power supply, thus the power of the heater 11 is changed and the temperature of the upper surface of the tray 13 is approximately to be the set temperature value. In this case, a control to the temperature of the upper surface of the tray 13 is realized by the temperature controller 16.
However, the MOCVD reactor operates in a vacuum environment. In the vacuum environment, radiation is a main way for transferring heat. The duration of transferring heat in the metallic chamber with a large capacity is long, and thus the time constant is increased. In this case, transferring the heat generated by the heater 11 to the upper surface of the tray 13 requires a certain time, which causes a lag on the change of the temperature of the upper surface of the tray 13.
In a heating up process in the MOCVD reactor, the lag temperature of the upper surface of the tray 13 is inputted into the temperature controller 16, and the temperature controller 16 controls the heater 11 to increase the current of the direct current power supply, which causes the heater 11 to overly heat and thus the temperature of the upper surface of the tray 13 exceeds the set temperature value. The temperature controller 16 then controls the heater 11 to decrease the current of the direct current power supply, to make the temperature of the upper surface of the tray 13 be decreased to the set temperature value. The lag temperature of the upper surface of the tray 13 is inputted into the temperature controller 16, which causes the power of the heater 11, controlled by the temperature controller 16, to decrease, and thus the temperature of the upper surface of the tray 13 is less than the set temperature value. Therefore, a temperature oscillation occurs in the chamber 10.
For the MOCVD process, merely a temperature change of 1 degree Celsius will cause a yield decreasing of at least 5%. Thus, it is a technical problem for those skilled in the art to obtain a steady temperature of the substrate to increase the yield of the MOCVD process.
For more technical solutions about the temperature control of the MOCVD reactor, reference may be made to Chinese Patent Application with publication NO. CN101906622A, which also fails to address the technical problem above.